One Tough Bite: T. Rex's Teeth Had Secret Weapon

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Secret structures hidden within the serrated teeth of
Tyrannosaurus rex and other theropods helped the
fearsome dinosaurs tear apart their prey without chipping their
pearly whites, a new study finds.

Researchers looked at the teeth of theropods — a group of
bipedal, largely carnivorous dinosaurs
that includes T. rex and Velociraptor — to
study the mysterious structures that looked like cracks within
each tooth.

The investigation showed that these structures weren't cracks at
all, but deep folds within the tooth that strengthened each
individual serration and helped prevent breakage when the
dinosaur pierced through its prey, said study lead researcher
Kirstin Brink, a postdoctoral researcher of biology at the
University of Toronto Mississauga. [ Image
Gallery: The Life of T. Rex ]

The new study upends one from the early 1990s, Brink said.
Researchers first noticed these cryptic cracks on the tooth of a
T. rex cousin named Albertosaurus about
two decades ago.

Initially, the researchers thought the cracks were signs of
damage, likely acquired when the dinosaur ate a hearty meal. But
the new analysis finds that isn't the case, Brink said.

"I sectioned teeth from eight other theropods besides
Albertosaurus, and found that the structure is actually
in all theropods, and it's not actually a crack," she told Live
Science.

The study actually began with a Dimetrodon, a Paleozoic animal with serrated teeth
that lived before the time of the dinosaurs. When Brink sliced
the Dimetrodon tooth in half and compared it with the
serrated teeth of dinosaurs, she found they had different
internal structures.

"They look very similar on the outside," Brink said. "It's only
when you cut them open [that you see] that they're completely
different."

Curious, she obtained two to three teeth from eight different
theropods species, including
T. rex, Coelophysis bauri and
Carcharodontosaurus saharicus. She also looked at
specimens of theropod teeth that had not yet fully matured and
erupted past the gum line, meaning, "they had not been used for
feeding," Brink said.

An analysis using a scanning electron microscope and a
synchrotron (a microscope that helps determine the chemical
composition of a substance) showed that each tooth, even the ones
that had not yet erupted, had these cracklike structures next to
each serration, she said. This debunked the idea that the cracks
were artifacts of eating a meaty meal, she said.

Furthermore, each structure has a few extra layers of calcified
tissue, called dentine, under the tooth's outer enamel coating,
making it tough and hard.

"We proposed a developmental hypothesis that these are structures
created when the tooth is first forming," Brink said. "It
actually helps to deepen the
serration within the tooth and strengthen each serration and
the tooth overall."

Serrated teeth help animals pierce through flesh and hold onto
chunks of meat. The formations, which the researchers call "deep
interdental folds," strengthen the serrations. In fact, they
likely helped theropods survive as top predators for about 165
million years, Brink said.

Serrated teeth still exist today in Komodo dragons. However,
Komodo dragon teeth don't have deep interdental folds, nor do
they have the extra layers of dentine that would strengthen their
bite, Brink added.

She called the toothy finding fascinating and "unexpected."

"It's really cool that such a small, little change in the
tooth structure, a small arrangement of the dental tissues,
could completely change the ways these animals are living," she
said.